1. Field of the Invention
The present invention relates to an ink for ink-jet recording, a color filter of a liquid crystal color display device used in color televisions, personal computers and the like, a process for producing the color filter, and a liquid crystal panel employing the color filter.
2. Related Background Art
A color filter is one of the important parts of a liquid crystal color display device. This filter is so constituted that many pixels of three primary colors of red (R), green (G) and blue (B) are arranged repeatedly. With development of personal computers, especially portable personal computers, liquid crystal display devices, in particular liquid crystal color display devices, are increasingly in demand. For further popularization thereof, the cost of the liquid crystal display device, especially the relatively high cost of the color filter, should be reduced. For reducing the cost of the color filter while retaining the required quality, various color filter production processes have been investigated. Typical production processes of color filters are explained below.
A first process employed most widely is a dyeing process. In this process, a water-soluble polymer for dyeing is sensitized by addition of a photosensitive material, the sensitized polymer is patterned by photolithography in a desired shape on a transparent base plate, and the obtained pattern is dyed in a dyeing bath to obtain a colored pattern. This operation is repeated three times to produce an RGB color filter.
A second process employed relatively widely is a pigment dispersion process. This process is replacing the above dyeing process. In this process, a photosensitive resin layer containing a pigment dispersed therein is formed on a base plate, and the resin layer is patterned to obtain a pattern for one color. This operation is repeated three times to form an RGB color filter.
A third process is an electrodeposition process. In this process, a transparent electrode is patterned on a base plate, and the patterned base plate is immersed in a electrodeposition solution containing a pigment, a resin, an electrolyte and so forth to deposit a first color. This operation is repeated three times to form RGB color layers and then the colored layers are calcined, thereby forming a color filter.
A fourth process is a printing process. In this process, paints containing a pigment and a thermosetting resin are applied onto a base plate for each of the three colors of R, G and B, and the colored resin layer is cured by heating to form an RGB color filter.
The above processes, however, have many unsolved problems, as below. For example, in any of the above processes, a protection layer is generally formed on the colored layer. And what is common to these processes is that it is necessary to repeat the same operation three times for formation of R, G and B, which increases the production cost inevitably. The larger the number of steps, the lower would be the yield, disadvantageously. Further, the third process is not applicable to a TFT color display device owing to the limited formable pattern with the present technical level. The fourth process has drawbacks of low resolution and poor smoothness, and thus is not suitable for fine-pitch pattern.
To offset these disadvantages, ink-jet systems are proposed for producing a color filter (see Japanese Patent Application Laid-Open Nos. 59-75205, 63-235901, 1-217302, 4-123005, etc.). In these systems, coloring liquids (hereinafter referred to as an "ink") containing respectively a dyestuff of red (R), green (G) or blue (B) are ejected through a nozzle onto a filter base plate, and the deposited inks are dried to form pixels, thereby forming a color filter. With this system, the colored layers of R, G and B can be formed in one step, and the inks can be deposited selectively on pixel formation portions without waste of inks, so that productivity can be improved and production cost can be reduced.
The ink for color filter production by the ink-jet system desirably satisfies at a higher level the requirements for characteristics shown below:
(a) high transparency of the pixels (colored portions) of the color filter, PA1 (b) less areal spreading of the pixels with lapse of time (hereinafter referred to as "bleeding"), PA1 (c) high adhesiveness of the pixels, PA1 (d) high light-fastness of the pixels of the color filter, and PA1 (e) high ejection stability in ink-jet recording system.
The production of a color filter by use of an ink-jet system is greatly different from conventional color filter production processes, for example as shown in FIGS. 3A to 3E, in that an ink 24 containing a dye in a high concentration is applied selectively onto pixel portions on a base plate 1 (FIG. 3A) and a solvent or the dispersing medium (water, an organic solvent, etc.) is evaporated to form pixels (FIG. 3C). FIG. 3B shows a state where the ink 24 is just applied and FIG. 3D shows a state where a pixel is normally formed. However, as shown in FIG. 3E, it has been found by the inventors of the present invention that the dyestuff may crystallize out from the ink 24 applied on the base plate during drying to lower a transparency of the formed pixels, or may cause bleeding of the pixels by migration of the pixel-forming dye with lapse of time owing to incomplete evaporation of the solvent. The remaining residual solvent in the pixels may lower the adhesiveness to the base plate by an interaction with the base plate, or may impair light-fastness owing to influence of active oxygen formed by thermal decomposition. Therefore, it is preferable that the ink for color filter formation preferably should satisfy the above requirements (a) to (d) at a high level. Further, it is needless to say that the ink for an ink-jet system should be ejected stably. The inventors of the present invention have investigated inks having the above characteristics. Consequently, it have been found that an ink comprising a pyrazolone dye satisfies the requirements for characteristics (a) to (e) mentioned above at a higher level as an ink-jet ink for formation of a green pixel in a color filter.